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Nielsen has been Kelly's right-hand woman since before he was confirmed to the secretary post

A cybersecurity and preparedness expert, she also has worked at DHS before

Washington (CNN)The woman nominated to replace John Kelly as secretary of the Department of Homeland Security, Kirstjen Nielsen, faced senators who will vote on whether to confirm her for the first time on Wednesday, largely pledging to carry on her predecessor's legacy.

That extended to Kelly's promise a border wall would be more limited than the one pledged by President Donald Trump.

"There is no need for a wall from sea to shining sea," Nielsen told the Senate Homeland Security and Governmental Affairs Committee, echoing a Kelly quote from earlier this year and his statements that border security would be a tailored approach that includes heavy use of technology.

Nielsen also pledged she would say something if she felt a policy announced by the White House was illegal or detrimental to the department.

"I fully intend in all cases and in all ways at all times to fully comply with all laws. I would expect the same of any employee or member of DHS," Nielsen said.

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"I would definitely tell the President if I thought a particular policy violated the laws of our country," Nielsen said. "But perhaps more importantly, it would be my intention in every instance to speak with him and other White House staff prior to any announcement of policy to make sure they understand both operational constraints, legal constraints, resource constraints and the views and insights of other stakeholders that would need to be part of its implementation."

Nielsen has been Kelly's right-hand woman since before he was confirmed to the secretary post. She served as his guide through his own confirmation hearings, was his chief of staff at DHS and followed him to the White House to be the deputy chief of staff when he took on the White House chief of staff job.

Nielsen avoided any major confrontations and appeared on track for confirmation by the Republican Senate.

Trump nominated Nielsen last month to replace Kelly. If confirmed, she would be the first former secretary who has previously worked at the department.

Johnson focuses on mass violence

Johnson spoke about last week's attack in lower Manhattan and the suspect's consumption of ISIS how-to manuals, asking Nielsen if she'd support limitations on what kinds of content can be posted on the internet. Nielsen left the door open.

"I would offer that I think we need to have a serious discussion, frankly, in conjunction with the executive branch and legislative branch, to look at this issue of content," Nielsen said.

In his opening statements, Johnson noted the issues DHS faces, including cybersecurity, hurricanes, illegal immigration and drug smuggling -- but took time to focus on one issue in particular: mass killings.

He noted the shooting in Wisconsin at a Sikh temple that killed six people in 2012, and then listed virtually every mass killing since. The nearly 20 killings he listed included the shooting at Sandy Hook Elementary, the Boston Marathon bombing, the shooting at a Charleston church, the movie theater shooting in Aurora, Colorado, the San Bernardino terrorist attack, the Pulse Nightclub shooting, and the recent killings in Las Vegas, New York City and Texas.

Johnson said his list included the deaths of 262 Americans and more than 1,000 wounded, and held a moment of silence.

"Later Sunday evening, my 34-year-old daughter asked me the questions we are all asking ourselves: What is happening; why is this happening; what can we do about it? Those are the questions the next Department of Homeland Security secretary will be asked to address," Johnson said. "It will not be an easy task."

Immigration and DACA

Neilsen also said recipients of Deferred Action for Childhood Arrivals, which the Trump administration is ending, deserve a "permanent" answer, without advocating for a particular version.

"I believe that we must, and we owe it to them, to find a permanent solution. It's no way to live a month, two months at a time," Nielsen said.

Nielsen committed that DACA recipients would not be a priority for immigration enforcement if they lost their status and that their information would be not shared with ICE outside of limited national security cases.

She also committed to "look into" any leniency with the October 5 deadline for renewals, which more than 20,000 recipients did not meet to extend their status. That went farther than the administration had previously, when it decline to extend the deadline.

"I would commit to you to look into it," Nielsen said. "I'm not familiar with those specific numbers, but if there are extenuating circumstances we should take into consideration, I would commit to look at it."